Apparatus for and method of percussive welding



'AIB. WHITE APPARATUS FOR AND METHOD OF PERCUSSIVE WELDING Filed May 7,1946 June 21,- 1949.

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A. B. WHITE APPARATUS FOR AND METHOD OF PERCUSSIVE WELDING Filed May 7.1946 5' Sheets-Sheet 4 fig/0.

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ATTOR Y A. B. WHITE June 21, 1949,

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Patented June 21, 1949 APPARATUS FOR AND METHOD OF PERCUSSIVE WELDINGAlfred B. White, Murrysville, Pa., assignor to Westinghouse ElectricCorporation, East Pittsburgh, Pa., a corporation of PennsylvaniaApplication May '7, 19%, Serial No. 667,761

My invention relates, generally, to welding, and it has reference, inparticular, to apparatus for, and a method of, percussive welding.

Generally stated, it is an object of my invention to provide percussivewelding apparatus which is simple and inexpensive tomanufacture, and issafe and reliable to operate.

More specifically, it is an object of my invention to provide forpercussively welding members which are prepositioned in engagement, bydischarging an electrical impulse therebetween, and applying an upsetblow in timed-relation to said impulse.

I is an important object of my invention to provide for using a weldingtransformer to couple a condenser discharge circuit to members which areto be percussively welded, in order to prevent dangerously highpotentials from existing between the members.

Another object of my invention is to provide for using a relativelylight contact pressure between the members which are to be percussivelywelded when the flow of welding current therebetween is initiated, andfor applying a relatively high upset pressure in predetermined timedrelation thereto.

Yet another object of my invention is to provide for increasing theeffective value of the weld current obtainable by the discharge of acondenser in a percussive welding system.

It is also an object of my invention to provide for percussively Weldingparts by using the stored energy of a condenser charged to a relativelyhigh potential, while maintaining a relatively low potential differencebetween the parts to be welded.

It is also another object of my invention to provide for prepositioningparts to be percussively welded with a predetermined contact pressuretherebetween, and reducing the contact pressure immediately prior todischarging a condenser through the parts and applying an upset force.

A further object of the invention is to provide for mounting memberswhich are to be percussively welded in relatively light jaw memberswhich are freely movable relative to each other.

A yet further object of my invention is to provide an improved method ofpercussive welding which is safe and easy to practice, and whichproduces improved and reliable results.

Other objects will in part be obvious, and will in part be explainedhereinafter.

In accordance with one embodiment of my invention, the parts which areto be percussively 16 Claims.

welded together are positioned in engagement in relatively movableclamps or chucks which are connected to the secondary winding of awelding transformer. The primary winding of the transformer is connectedby an electric discharge valve to a condenser which is charged from suitable source of electric energy. A hammer is provided having fluidpressure means for retracting it and actuating it to strike an upsetblow against one of the clamps to force together the parts to be welded.An electromagnetic clutch retains the hammer in the retracted positionuntil the fluid pressure reaches a predetermined value and the condenseris properly charged. The hammer is then released, and in moving itactuates a switch which renders the electric discharge valve conductiveimmediately prior to the application of the upset force, whereby theparts are percussively welded together.

For a more complete understanding of the nature and scope of myinvention, reference may be made to the following detailed description,which may be studied in connection with the accompanying drawings, inwhich:

Figure 1 is a side elevational view of a percussive welding machineembodying its invention in one of its forms;

Fig. 2 is an enlarged horizontal sectional view of the magnetic clutchused to restrain the hammer on the machine shown in Fig. 1;

Fig. 3 is an enlarged end elevational view of the magnetic clutch takenalong the line III-III of Fig. 2;

Fig. 4 is an enlarged elevational view in section of the jaw structureof the machine shown in Fig. 1 taken along the line IV-IV of Fig. 5;

Fig. 5 is an enlarged end elevational view in section of the jawstructure taken along the line V-V of Fig. 4;

Fig. 6 is an enlarged rear elevational view of the switch means shown inFig. 1;

Fig-'7 is an enlarged end elevational view of the switch means shown inFig. 6;

Fig. 8 is an enlarged partial front elevational View of the weldingmachine shown in Fig. 1, broken out in part to show details of the jawoperating mechanism;

Fig. 9 is an enlarged end elevational view of the jaw mechanism, takenalong the line IX-IX, of Fig. 1;

Fig. 10 is a diagrammatic view of a percussive welding system embodyingthe invention of Figs. 1 through 9, and

Fig. 11 is a diagrammatic view of welding ap- 3 paratus embodying theinvention in another of its forms.

Referring to Fig. 1 the reference numeral l2 may denote, generally, apercussive welding machine, wherein a jaw mechanism l3 includingrelatively movable chucks or clamps l4 and I5 may be mounted-ion asupport l6 attached to 'abase IT, for-positioning members which are tobe percussively welded together. A fluid pressure cylinder I9 havingforward and reverse fluid pressure connections and 2|, respectively',maybe provided for actuating a piston rod- 22 'ior may be'efiected bymeans-of a fluid pressure op-' erating mechanism 21 which may beprovided with-forward and reverse fluidpressure connections 28 and 29for actuating-a hollow piston rod 30 uponwhich the hammer may bemounted. A fluid pressure control switch 3! is provided with the-forward connection 28, and switch means32may be provided forcontrolling the application of an-impulse of electricalenergy to the.members to bewelded in response to the movementof the hammer 25.

An electromagnetic clutch 34-may be provided forretaining the piston rodin the retracted position. until predetermined operating conditions,which will be explained'hereinafter, are fulfilled. By. mounting theclutch 34 on longitudinal supports 35 with a predetermined degree ofmovement,-the fluid pressure operating mechanism 21 may be utilized toapply a predeterminedcontact pressure to the members to be weldedprior-to the delivery of-an upset. The clutch 34 may, for example, beconnected to an elongated rod 31 whichpasses through the hollow pistonrod 30 andengage the clamp l4-,--so as to bias the clampl4 towardstheclamp l5 A stop 23 maybe-utilized for while the clutch holds thehammer 25 against Y movement under the action of the-fluid pressure inthe forward direction in the fluid pressure operating mechanism 21'.

Referring to Figs. 1,2 and 3, it maybe seen that the clutch '34 maycomprise; for example, a rectangular body 40- of magnetic materialhaving an annular groove 4| therein, in which maybe positioned anoperating winding 42- for producing thenecessary magnetic flux. Theannular groove ll-may be partially enclosed by means of. a face plate 44of a magnetic material of high permeability having a central opening 45which defines with a central ring 46 also of high per.- meability, aperipheral air gap-4'L- The hollow connecting rod 30 of the fluidpressure actuating mechanism 21 may be provided with an armature 49 ofhigh permeability magnetic material which may be disposed to bridge theperipheral airgap 41 for retaining the piston rod 30 in the retractedpositionwhen the operating winding 42 is energized.

The magnetic clutch 34 may be movably mounted on the supports 35 bybeing positioned on spacers 50 which may be secured to the supports 35by means of nuts 5|. may pass through openings 53in the body member4110f the clutchand project slightlytherebeyond, so as to provide alimited amount of longitudinal movement of the clutch relative to Thespacers 50 I thereon in paired relation.

the supports. The rod 31 may be connected to the body member 40 in anysuitable manner and it may, for example, pass through a central opening55 in the body member, wherein it may be cured by a set screw 56. Bysuch an arrangement the fluid pressure mechanism 21 may be adapted tobias the clutch. to the right under fluid pressure action, so that therod -31"forces the clamp [4 toward the clamp l5.

Referring to Figs. 1, 4 and 5, it may be seen that. the chucks or clampsl4 and 15 may comprise upper and lower insulating supports and SI havingrelatively movable pairs of upper and lower jaw memberscfl, 63 and 54,65 mounted The lower support 6| may be stationary being, for example,secured to thezupper portion of the base IT. The jaw members 63 and 65may be secured by screws 66 to the insulating support 6|, which is inturn secured to the base by means of screws 68.

The upper insulating support: 50 may bemovablein the vertical directionrelative to the lower support 6!, being,- for example, secured by screws69 to a backplate 'lfl 'which may be actuated by-means' of a link-(shown in Figs. 8 and .9) connectedto the support SU'by meansoia pin Il. The back plate 10 may be-provided with guides l2 for-limitingthe-upper support 60 tola movement in the vertical direction, The upperjaw members 62-and .M maybe secured by. means of screws 13 to theinsulating supporttilli The pairs of jaw-members 62,-.63 a'nd 64, 65comprising the clamps l4 and 15 may be movable relative to each other ina longitudinal direction. This movement maybe provided Icy-mounting theindividual jaw members on the insulating .supports 60 and-5i inchanneled supports 11' which are securedto the insulating-supports- 60'and Bi, and which may be provided withinturned edge 'portions (-8"disposed to be positioned in longitudinalgrooves 19 along theopposite'edges of the jaw members.= Bearing members may be interposedbetween the jaw unembers and their respective supports to providefreedom of movement of the-jaw members. Each ofthe jaw members may beprovided with-an arcuate recess 81* having end-shoulders B2 to providefor securing charged members to be welded, such as sectionsfo-r-thetube-orthe like. Means such .as the keys -83 may: be-positioned'intransverse supportinto engagementwith adjusting rneans- 8!! which ismovable "in accordance with the position of the jaw-members 64 and-55.'A-contact member-- may be mounted'on the contact support 81 forengagement with the hammer 25' to complete-a circuit to a conductor SIfor efiecting the discharge of electrical energy throughthe par-tstobe'welded, in a manner which will-be explained in detail hereinafter.

Refer-ring to Figs.-l,' 8 and-9, itmay be seen that the jawmechanisr'n-13 may comprise a toggle plate 93 -'=which"may-be mounted on ahorizontal shaft: Mbetweenxfrontand rear plates 95 and 96onthevsupport'. l8, ito: provide with a link 91 mounted on the: pin 1 Ian operating connection: $9, I which: raises and. lowersthe. upper Jawback .plate 10in response-to movement. of

a head 98 which may be threadedly mounted on the piston rod 22 of thefluid pressure operating mechanism I9. A spring 99 may be connected toan arm I09 secured to the shaft 94, and to a pin ill of the jawmechanism for biasing the upper support 60 to the downward position. Anextension I02 may be provided on the head 99 for operating a controlswitch I03 which serves to maintain a holding circuit for the clutch 34and prevent energization of the jaw members, unless the jaw members arein the closed position.

As shown in Figs. 1, 8 and 9, a yoke I04 may be utilized for positioningthe jaw members 64 and 65 of the clamp I4 in accordance with themovement of the head 98 when the fluid pres-. sure operating mechanismI9 operates to retract the piston 23 and raise the upper jaw back plateI0. The yoke I04 may comprise a pair of depending legs I05 and I06positioned in spacedrelation and pivotally mounted in the base I'I' ofthe machine on a bracket I01. The legs I05 and I06 may be positioned inrecess I08 in the jaw members 64 and 65, and may be connected at theupper end by means oi a connector I09 which is engaged by the head 98when the piston rod 22 is retraced. The jaw members 64 and 65 may bebiased towards the jaw members 62 and 63 by means of the elongated rod31 which may be positioned in recesses H0 in the ends of the jaw members64 and 65.

Referring to Fig. 10, the reference numeral I29 may denote, generally, apercussive welding system, wherein a condenser I22 is disposed to becharged from a source of alternating current I23 through rectifyingmeans comprising electric valves I 24, I25 which may be connected to thesource I 23 by means of a transformer I26 and a cutout switch I21.

The condenser I22 may be connected through a step-down weldingtransformer I28 to the jaw members 65 and 63 by means of inverselyconnected valves I30 and I3I of the arc discharge type. An electricvalve I32 may be provided for energizing the ignitor I33 of the valveI33 in response to the operation of the switch means 32, which may beactuated in predetermined time relation to the upset blow by the hammer25 as it is moved by the fluid pressure means 21 to engage the jawmembers 64 and 65.

In order to prevent operation of the welding system until the condenserI22 reaches a predetermined value of charge, a neon discharge valve I 35may be utilized in connection with a discharge bias resistor I36 forapplying a negative bias to the control grid I38 of a control valve I39which is normally rendered conductive to effect energization of theoperating winding I40 of control relay I42. The valve I35 also providesa bias control voltage to the control grids I43 of the rectifier valvesI24 and I 25 to terminate charging of the condenser. A condenser I3'Iholds the bias voltage for a predetermined time. An additional controlrelay I44 may be provided, which is normally energized through a controlvalve I 45 after the control relay I42 operates to close contact membersI42a and apply a positive bias to the control electrode I46.

Operation of the fluid pressure actuating means I9 and 21 may beeffected by means of forward and reverse fluid pressure valve devices Iand I5I, which may be connected to the forward and reverse connections20, 28 and 2|, 29',

and provided with operating windings I52 and I53, respectively, foroperating the devices to alternately admit fluid pressure to the forwardand reverse ends of the fluid pressure actuating means I9 and 21 underthe control of the control relays I42 and I 44. The magnetic clutch 34may be energized from the source I23 through a control transformer I55and a secondary control transformer I51, and an associated rectifierbridge circuit I58.

When the disconnect switch I2! is closed, the magnetic clutch 34 isimmediately energized. When the start push button I60 is operated, theoperating winding I40 of the control relay I42 is connected across thesecondary winding of transformer 555 through the control valve I39,which is immediately rendered conductive. The control relay H22operates, and applies a positive bias to control electrode I46 of thevalve I45 through the rectifier device I62, thus rendering the valve I45conductive. The operating winding !63 of the control relay I44 is,thereby, energized and the control relay I44 operates, providing aholding circuit around the start push button I60 through normally opencontact member I441).

At the same time, an energizing circuit is provided for the operatingwinding I65 of the primary switch I66 through normally open contactmembers I 44a. The primary switch operates and connects the primarywinding I61 of the transformer I26 to the source through contact memberI65a. Since the valves I24 and I25 have zero bias, the condenser I22charges.

As soon as the condenser I22 reaches a predetermined value of charge,the neon discharge valve I35 breaks down and a discharge current flowsthrough control resistor I36. This produces a voltage drop across theresistor I36 in such a direction as to apply a negative bias voltage'tothe control electrode I38 of the electric valve I39 through which thecontrol relay I42 is energized. The valve I39 is rendered nonconductiveso that the control relay I42 returns to the deenergized position.

The bias voltage from the resistor I36 is also applied to the controlgrids of the valves I24 and I25, thereby preventing further charging ofcondenser I22. Condenser I3'I holds blocking bias for a short time afterdischarge of I22 to prevent conduction in I24, I25 until switch I66 isdeenergized.

An energizing circuit is now completed through normally closed contactmembers I42b and normaily open contact members I440 for the operatingwinding I52 of the forward valve device I50. The valve device I50 isthereby operated, and fluid pressure is applied to the fluid pressureactuating devices 27 and I9 in the forward direction, so that the upperjaw member support 69 is actuated downwards, and the rod 31 which isconnected to the magnetic clutch 34 restraining the hollow piston rod 30urges the jaw members 64 and 55 longitudinally towards the jaw members52 and 63 which are thereby backed up solidly against the stop 23.

As soon as the pressure in the fluid pressure operating means 21 reachesa predetermined operating value, the pressure switch 3I is operated andthe energizing circuit for the electromagnetic clutch 34 is interrupted,since control switch I03 responsive to the position of the jaw membersis already in the open position. Accordingly, the piston rod 30 isactuated to move the hammer 25 toward the right to strike the jawmembers 64 and 65 of the clamp I4.

As. :soonasnthe hammer 25' engages @the :con-.

tactmember 90 sot-the switch .means-. 32,.-1 the negative biasvoltage onthe control. electrode I69?- of. the: control; valve 1 I32 is reduced:sufliciently' to permitsthe discharge device I32 to conduct and renderthe are discharge device I30. conductive.

The condenser; I 22 thereupon discharges through i gether .themembers-being welded. Thismccurs preferably during; the first half cycleof the com, denser discharge;

When the control relay I reaches the deenergized :position, theoperating winding I53.- ofrzthe reverse' valve device .I5I is energizedthrough contact member Ind and control. switch I58.'so-thatvthezfluidpressure operating means I9 and 2!- retract the jaw. members andthe.hammer-to. provide for a subsequent operation.

Referring to Fig. 11, the reference numerals IlsII and I'll may denote,generally, the upper and lowerwsupports of awelding machine. havingmeansmuch as fluid pressuredevice I12: for operating-the :upper supportI10, towards. and. away from' the lower support IH. Adjustable jaws[14,.415- may besecured to the supports I" and I:'I-I*, respectively,,for securing members'l'll' and H8 which 816130.136 percussively weldedto each.

other.

The lower'jaw I may be resiliently mounted,

being for example,.mounted in a sleeve I80 which may lee-electricallyinsulated from the support III. by: meansof an insulating sleeve I82.andzanirisulating. washer I83. The jaw I'Is5 may'be provided with athreaded stem 5 I 85 .which projects through an. opening I 86' 1 in thebottom. or the sleeve I80.w. A spring I87 may bezinterposedibetween-thebottom of the sleeve I80 and the jaw I15, and nut I88 may be provided onthe. stem I85- for adjusting-the .tension' of the spring I81. Itodifieren-t predetermined values. The inertiav .of. the jaw I15 may bevaried by using nuts I88- of diiferentweights.

The upper jaw I14 may be slidably mounted in a sleeve I99 secured to theupper support IN. A.

spring [9i may be provided for normally: biasing the upper jawll ldownwardly against the lower jaw. Il.5,$:-to maintain a predeterminedminimumcontact pressure between the members I1 1 and [Hi-.-

Aihammer' I-93 may be slidably positioned in the sleeve-199x01 applyinga percussive blow to the upper. end of the jaw IN. The hammer maycomprise ahead portion I94 having an elongated stem 195 with a recesshaving a shoulder I96 adjacent the-upper -end for engaging a latch I91which may be adjustably mounted on theframe- I98 0f the welding machineanddisposed-"foroperation-in any suitable manner to release the hammer.A spring 200 may be positioned around the stem. l95 -for-bia'singthehammer I93 downwardly tostrike the upper jaw I";

Means such as the condenser 202 may be pro-- vided for'effecting a,rapid discharge of electrical energy between the'members I" and 4 I8inorder to weld them-together. The condenser may be chargedfrom-any.suitable source-0t electrical energy-which :may be represented by thebatters 203.? An impedance-.2045 lmay. be. provided .1111.series-circuitrelationwith the. condenser-2w and thesourceifliilforlimiting. thedischarge of the electricahenergy-from thesource when the con.- denser i-sibeing discharged.

Inversely connectedvalve devices 205' and 28-5 ma-y be.-provided in:conjunctionwith a control valve 1E1:- ihavin'g-a control electrode 201afor discharging the condenser 202 through the primarvwinding-wfl of aWeld-ing transformer 20-9;-"havinga secondary winding 2 I I] connectedto f the jawxmembers I'M and I15.

Iri'orderto effect discharge of the condenser 292 in timed relation tothe hammer blow struck by the hammer I93, a control switch 2I2 may bepr'ovicledr- Either entire switch 2I'2, or projection 2 I-8 'ma ybe-adjustable for effecting different discharge time IZOntTOL- Thiscontrol switch may comprise-a pair of normally spaced contact membersM3. and. 2M which may be adjustabl-y mounted inanysuitable manner inspaced and insulated relation upon the sleeve I- by meansofinsulation-2l5 and screws -2I6. A projection 218 may ;beprovided inconnection with contact member 2 l4 for-engagement with the head of thehammer-19$ as it-moves-to strike the jaw member I14. By connectingthecontact members H3 and 2M acrossa portion-of a control resistor 220'in the grid circuit-of the valve 201, the discharge device-206--inay berendered conductive as soon as the head I94=of-the-hammer strikes theswitch project-ion 2 I8 and causes the negative bias applied to thecontrol'electrode 201a to be reduced sufficiently. A condenser 222'between grid and switch 2 I 2 permits momentary short: circuiting ofgrid 'blas without'susta'ined current drain. A

"shunt resistor 223- bleeds charge from the capacitor between welds;

In operatiomfluid pressure may be applied to the fluid pressure deviceI12 to raise the upper support 110. This carries the hammer I93 upwardlyso that the latch I91 enters the recess I96 and separates the jaws forunloading or loading. Fluid pressure may be then applied so as to forcethe upper support ITO. downwardly until the members-I71 and H8 in thejaws Inland I15 are in engagement.v Thehammer I93 is retained in theretracted position'by the latch I91.

Whenthelatchfl'fis re1eased,.'the hammer I93 is also released and isactuatedby the spring 2B9 towardthe jaw member I'l4lto strike apercussive blown When the head of the, hammer engages the switchprojectionZIB, the contact members 2I3 and 2, are connected and thecondenser 20! is dischargedto' provide anelectrical impulse between themembers IIJ and i118 immediately prior to the impact oi the hammer I93on the upper jaw member I14. Accordingly, the surfaces ofv the membersI'lland I18 are rendered. molten, and almost.instantaneously apercussive force is applied to produce .an upset and effect. a weldbetween the members.

From theabove description. and the accompanyingdrawingadt will be seenthat I have provided .welding. apparatus and a method of welding inwhichthe voltage whichcan appear at theelectrode jaws,.andthe.durationof the voltage are both so .smallflthat the; process is electricallysafe... The process .is also mechanically safe since the movement of thejaws is relatively slight. The hammer which travelsat a high speed andhas a relatively long path of movement, is separate from the. jaws: andmay-thus be readily shielded. By using, a weldin ;transformer: tocouple. the con denseresourcerof weldingenergy, to the members tobe-weldemthevalue the :welding current may be very high while thecondenser is operated at an efiiciently high voltage and a relativelylow frequency and current. The use of a welding transformer also permitsthe use of a relatively small and, therefore, low reactance loop in thatportion of the welding circuits which carries the relatively high valuesof welding current.

The condenser discharge current is determined by the equivalentinductance of the welding circuit, plus the inductance of theconnections to the condenser. The primary current depends principally onthe square root of the total reactance, and the secondary or weldingcurrent is greater than the primary current by the ratio oftransformation. The square root of the total inductance will normally begreater than the square root of the inductance of the condenserconnections, but will normally be much less than the ratio oftransformation times as great. It will, therefore, be seen that it ispossible to obtain much higher values of welding currents by using awelding transformer than if the condensers were discharged directlybetween the pieces to be welded. This is an important feature, since itis highly desirable to obtain an are over the entire weld surfaces, andthe area covered by the arc is invariably the function of the currentdensity.

In operation, the efficiency of the method proposed in my invention isreadily illustrated by the fact that better welds may be made with onecondenser unit of 120 microfarads charged to 2500 volts than could bemade with four units charged to the same voltage in the case of thedirect connection. An additional advantage of the present method lies inthe relative flatness of the voltage- 1 current characteristic which maybe obtained. The short circuit current, for instance, may be two or moretimes as great as the current during.

Furthermore, enough contact pressure may be used between the weldsurfaces so that the current in the welding circuit builds up to thepeak arcing current before the arc is established. In addition, sincethe current tends to drop rapidly as the voltage across the weld piecesrises, any tendency for the arc to overheat a point on the weld surfacesor to climb the higher edges of the weld pieces causes the arcingcurrent to reduce and the arc to transfer to cooler surfaces and/ or ashorter path.

The system of my invention is extremely flexible. By changing thetransformer turns ratio, and without necessarily changing either thesize of the condenser, or the voltage at which it is operated, it ispossible to change from a highly damped unidirectional discharge to arelatively high frequency oscillating discharge. Since the position ofthe switch means 32 is maintained in the same relative position to thejaw members regardless of differences in the sizes of the pieces to bewelded, sa 'sfactory welds may be easily made on pieces of varyingdimensions without requirin complicated adjustments between welds.

Discharge frequencies in the range of 50 to 3000 cycles per second maybe used effectively, the higher frequencies being more desirable whenwelding materials have widely different melting points and/ or thermalcapacities. Frequencies in the lower range may be used in welding copperto copper, or steel to steel. In practice, I have used '10 a relativelynarrow range of frequencies of from about 300 to 500 cycles per secondwith a wide variety of materials and with settings of the switch meansvarying as much as one quarter of an inch. In general, the switch meansmay be adjusted so that the hammer strikes the upset blow during thefirst half cycle of the condenser discharge, preferably between the peakand the end of the first half cycle. Satisfactory welds have been madeon many combinations of materials under these conditions, using hammerspeeds of from about 100 to 500 inches per second.

Since certain changes may be made in the above described construction,and different embodiments of the invention may be made without departingfrom the spirit or scope thereof, it is intended that all the mattercontained in the above description and shown in the accompanyingdrawings shall be considered as illustrative and not in a limitingsense.

I claim as my invention:

1. A method of welding which comprises, prepositioning a pair ofmetallic members with sur-- faces in contact, passing an electricaldischarge from a condenser therebetween sufficient to produce a fluidcondition of the members at the contacting surfaces, and applying arelatively sharp blow to at least one of the members such as to forcesaid one member against the other member and force the contactingsurfaces together between the peak and the end of the first half cycleof the condenser discharge.

2. In a method of percussive welding electrically conductive membersWhich comprises the steps of positioning the members with surfaces to bewelded in contact, connecting a charged electrical condenser between themembers so as to produce a sudden discharg of electrical energy betweensaid surfaces, and striking one of the members a sharp blow to force itagainst the other member during the latter portion of the discharge ofelectrical energy between said surfaces to force the surfaces together.

3. The method of percussive welding which comprises, positioning a pairof metal members in engagement in substantially the position in whichthey are to be welded, passing a predetermined condenser dischargewelding current inrpulse through the juncture of said members, andapplying a relatively sharp hammer blow to one of the members in adirection to force it toward the other member in'predetermined timedrelation to said impulse and during the first half cycle thereof toforce said members together.

4. Percussive welding apparatus comprising, relatively movable clampmeans arranged to hold members which are to be welded, means operable tobias the clamp members to position the members to be welded inengagement with each other, circuit means including a stored energysource of electrical energy, means operable to apply a hammer blow tothe member in the movable one of the clamp means in a direction to forceit against the other member, and switch means actuated by the said meansconnecting the circuit means in circuit relation with the members intimed relation to the hammer blow.

5. Welding apparatus comprising, a fixed clamp and a relatively movableclamp arranged to hold and position members to be welded in contactingJrelation, means operable to urge the movable including a condenserdisposed to be charged from a source of electrical energy, and switchmeans responsive-to movement of the hammer to strike the movable clampoperable to connect the circuit means between 'themembers to be weldedin timed relation to initiate discharge of the condenser immediatelyprior to the time when the hammer strikes the movable clamp.

6. Percussive welding apparatus comprising, pairs of jaw members forholding members to be welded, means biasing the 'jaw members to maintainthe members inengagement, a hammer slidable axially of'the'jaw members,means operable to apply an accelerating force for actuating the hammerto strike one of the jaw members and force it toward the other jawmember to apply an upset force to the members to be welded, meansresiliently supporting the other jaw memher, and switch means actuatedin response to movement of the hammer for controlling the energizationof the membersto be weldedin timed relation to the application of theupset force.

'7. Percussive welding apparatus comprising, two pairs of jaw membersoperable to clamp members to be welded, a stationary Support mountingone of the jaw members of each pair, a support movable axially of thejaw members mounting the other jaw member of each pair, fluid pressuremeans/operable to move the movable support axially of said other jawmembers, a hammer disposed to'be actuated to a retracted position inaccordancewith .operation'of the fluid pressure means toseparatethe jawmembers, retaining means operable'ito maintain the hammer in theretracted position", control means operable to effect release of thehammer'from the retaining means for striking oneof the pairs of jawmembers, and switch meansiactuated by the hammer to connect the membersto be welded to a stored energy sourceof welding current.

8. In a welding system, a condenser, circuit means connecting thecondenserto a source of electrical energy for effecting the'chargingthereof, relatively movable clamp members for gripping members to beweldedtogether, a welding transformer having a secondary-winding con- 1nected between theclamp membersand a primary winding, valve: meansconnectedbetween the condenser and the primary winding for dischargingthe condenser, switch means operable to render the valve meansconductive, a hammer operable to effect operation of the switch meansand to strike'oneof the relatively movable clamp members to-force ittoward the other clamp member and provide an upset force to said membersto be welded in the first half cycle of the discharge of the condenser,

9. A percussive welding system comprising, a pair of relativelymovable-jaw members arranged to hold members to be welded, a movablesupport for one of the jaw members, fluid pressure means operable toretract "saidsupport axially of the jaw members and return it to'theweld position, means biasing the one jawmember' relative to the movablesupport and toward the-other jaw member, a hammer carried by the supportand normally biased toward said one jaw member, means operable to retainthe hammer in a retracted position when the support is returned to theweld position and actuable torelease the hammer for providing an upsetblow, switch means carried by 'the support actuated by the hammer whenltls'IBlBK- ed from the retracted position, and circuit means includinga weldin transformer connected tov the jawmembers, a condenser source'ofstored electrical energy and 12 electric valve means rendered conductiveby the switch means to provide an impulse of electrical energy having afrequency of from 50 to 2000 cycles per second between the members intimed relation to the application of the hammer blow thereto.

10. A percussive welding machine comprising, a pair of supportsrelatively movable in one direction, a pair of clamps relatively movablein a different direction, each of said clamps comprising paired jawsections mounted one on each of the supports, means providing a stop forone clamp, actuating means operable to bias the other clamp toward saidone clamp, a hammer operable to strike said other clamp an abrupt blow,means including a condenser disposed to be charged from a source ofelectrical energy and valve means operable to connect the condenserbetween said clamps for providing a relatively high frequency discharge,and switch means actuated in response to predetermined movement of thehammer to render the valve means operable.

11. In a welding system, clamp means securing pieces to be welded inwelding position, a fluid pressure operated hammer actuable to providean upset force between the pieces, means responsive to the applicationof fluid pressure to the hammer to initially bias the pieces together,and means responsive to movement of the hammer toward the pieces forefiecting a discharge of welding current between the pieces having afrequency of from 300 to 500 cycles per second, said means beingarranged to efiect'such discharge in such timed relation to the hammerblow that the hammer blow occurs during the first half cycle of saiddischarge.

12. In a welding system, clamp means securing members to be weldedinitially in engagement, a transformer having a secondary windingconnected between said means and a primary winding, circuit meansincluding a switch for connecting a source of stored electric energy tothe primary winding, switch means operable to efiect operation of theswitch to connect the condenser to the primary winding, and a hammeroperable to actuate the switch means and apply an upset force to one ofthe members to be welded to force it against the other member duringdischarge of the condenser.

13. Welding apparatus comprising, means actuable to clamp members to bewelded, means including a hammer and fluid pressure means operable toactuate the hammer to produce an upset between the members to be welded,means including locking means to retain the hammer in a retractedposition in opposition to the fluid pressure means, a condenser, meansfor charging the condenser, means responsive to a predeterminedcondition of condenser charge operable to prevent operation of the fluidpressure means, manual switch means operable to initiate charging of thecondenser, circuit means including switch means actuated by the hammerconnecting the condenser to produce a current impulse between themembers to be welded in timed relation to the upset produced by thehammer.

14. For use with percussive welding apparatus having relatively movablejaws for clamping members to be welded and a hammer arranged to strikeone of the jaws to produce an upset between the members, a weldingtransformer having a relatively small number of secondary turnsconnected between the jaws and a relatively large number of primaryturns, circuit means including an electric valve and a condenserconnected across the primary turns, control means responsive topredetermined conditions of charge of the condenser for effectingoperation of the hammer, and means responsive to operation of the hammerfor eifecting discharge of the condenser.

15. For use in percussive welding, a welding transformer having primaryand secondary windings with a high ratio of primary to secondary turns,relatively movable clamp means connected to the secondary winding andarranged to secure members to be welded in welding position, a hammeractuable to apply an upset blow to the members, fluid pressure meansoperable to actuate the clamp means to bias the members into ongagementand actuate the hammer, and control means including switch meanspositionable in difierent axial positions in accordance with relativeaxial positioning of the jaw members actuable in response to movement ofthe hammer to apply an upset blow for efiecting energization of theprimary winding.

16. In a welding system, clamp means operable to position members to bewelded in engagement, a transformer having a secondary winding connectedbetween said means and a primary winding, a hammer operable to strikeone of said clamp means to produce an upset between the members to bewelded, fluid pressure means operable to actuate the hammer, meansoperable to restrain the hammer and bias the clamp means toward eachother, a condenser, circuit means including a switch for connecting thecondenser to a source of electrical energy for effecting the chargingthereof, control means operable to eflect operation of the switch means,said control means being responsive to a predetermined condition ofcharge of the condenser for rendering the hammer restraining meansineffective whereby the fluid pressure means actuates the hammer, valvemeans connected in circuit relation with the primary winding and thecondenser, and switch means positionable in accordance with said oneclamp means actuated by the hammer to render the valve means conductivein predetermined relation to the hammer blow.

ALFRED B. WHITE.

REFERENCES CITED The following referenlces are of record in the flle ofthis patent:

UNITED STATES PATENTS

